Glycated haemoglobin, abbreviated HbA1c or A1c, is a blood test that estimates average blood glucose over approximately the last 3 months. It is used both to diagnose prediabetes and diabetes and to monitor glucose control in people already diagnosed.
What does HbA1c measure?
As glucose circulates in the blood, some attaches to haemoglobin in red blood cells. The higher blood glucose is over time, the higher the percentage of “glycated” haemoglobin. Because red blood cells live for approximately 3 months, HbA1c provides an overview rather than just a value at one moment.
HbA1c should not be confused with blood glucose measured at home or in a laboratory on a particular morning. For practical differences, see the guide to fasting and after-meal blood glucose.
HbA1c levels: normal, prediabetes, diabetes
- Below 5.7% – usually considered the normal range;
- 5.7–6.4% – a range consistent with prediabetes;
- 6.5% or above – a value consistent with diabetes, usually confirmed by repeating the test or using another test if there are no obvious symptoms.
These thresholds are useful, but do not tell the whole story. Someone with an HbA1c of 5.8% and abdominal obesity may have a different risk from someone with the same result but no other risk factors. Good interpretation considers the entire metabolic profile.
HbA1c targets for people with diabetes
For many non-pregnant adults with diabetes, a commonly used target is HbA1c below 7%, but this must be individualised. Some people may have lower targets if their risk of hypoglycaemia is low; others need less stringent targets, particularly if they are older, have other conditions or experience hypoglycaemia.
This is why it is not appropriate to compare your result directly with someone else's. Your target is agreed with your doctor, taking treatment, safety and quality of life into account.
When can HbA1c be less accurate?
HbA1c can be influenced by conditions affecting red blood cells or their lifespan. Examples include anaemia, recent blood loss, certain blood disorders, pregnancy, advanced kidney disease or some haemoglobin variants. In these cases, the doctor may recommend fasting blood glucose, a glucose tolerance test or glucose monitoring.
How often is HbA1c checked?
In people with stable diabetes, HbA1c is commonly checked at least twice a year. If treatment changes, levels are far from target or symptoms occur, more frequent testing may be recommended, usually every 3 months.
If you have received your result and do not know how to interpret it, the online test interpretation service can help put it into context alongside your blood glucose, lipid profile, liver function and other tests.
What should you do if HbA1c is high?
The first step is confirmation and assessment of the cause. Concrete interventions then matter: tailored nutrition, exercise, sleep, weight loss if appropriate and medication when indicated by the doctor. For many people, a diabetes nutrition plan and structured monitoring make a significant difference to the course of the condition.
